(3.)求下列极限:-|||-(1) lim _(xarrow infty )dfrac (1)(1+{z)^2} ;-|||-(3) lim _(zarrow 1)dfrac (z-i)(z(1+{z)^2)} ;-|||-(2) lim _(xarrow 0)dfrac (Re(z))(z) ;-|||-(4) lim _(xarrow 1)dfrac (zoverline {z)+2z-overline (z)-2}({z)^2-1}